Are you referring to the sill plates with the ali s3 strip on them? If so they are held in place by double sided tape and also they clip into the sideskirt along the base. You can pop off the bottom part using a small flathead, maybe tape along the skirt etc to avoid any damage. The black part at the base that folds over the sideskirt is the bit that needs popping off, just prise it up gently until that part pops off. It is held in place in about 6 places along the skirt. The rest of it is then held in place by the double sided tape. Use a heat gun to try and loosen the tape up without getting it close to your paint as it will damage it. It is not an easy part to remove without doing some damage because the plastic becomes very brittle it if hasn't been removed in 8+ years and it is easy to crack the lower part. Instead of using a flathead to pop it off then maybe try and use a long thin ruler or anything else that is long and thin which should help avoiding cracking the plastic.
It does seem a lot of effort to just clean behind them though. I would have thought you could get a brush down the sides to clean them up without removing them.
